And it was cold as a witch's teat,

“Teat” is an old-spelling for the modern word “tit.” (This book was published in 1951)

Cold as a witch’s teat, is a metaphoric idiom. Because witch’s are in connection to the devil (ruler of hell) and sell their souls to the devil, seemingly rendering them insensible and without feeling… thus the idiom was used by Holden, referring to the cold of December, being cold as a witch’s teat. Another decently relative idiom would be “as hot as the hinges of hell.”